Automotive fluid control system with pressure balanced solenoid valve

ABSTRACT

An automotive fluid control system with pressure balanced solenoid valve [ 24 ] and fluid mixing housing [ 22 ] is disclosed. The solenoid valve [ 24 ] is preferably used in an EGR (exhaust gas circulation) fluid control system, although the valve may be used in other vehicle fluid control systems, such as an engine block cooling liquid control system. A poppet member [ 84 ] of an EGR valve is pressured balanced such that only a light spring [ 170 ] and armature [ 88 ] are needed to control the positioning of the poppet member [ 84 ]. Magnetic and inductance sensors [ 184, 282 ] are used to accurately determine the position of the poppet member. The fluid mixing housing [ 22 ] homogeneously mixes first and second fluids. A portion of a main first fluid flow is funneled off and mixed in the housing [ 22 ] with a second fluid prior to being returned to the main fluid flow. Ideally, the housing [ 22 ] has a circumferentially extending channel [ 95 ] for intercepting, funnelling and mixing the captured portion of the main first fluid flow with the second fluid flow. Also, a solenoid subassembly [ 82 ] is disclosed which can mate with a variety of different valve housings [ 22 ] and which is adapted to mount on various engine configurations.

The present application is a continuation-in-part of U.S. Provisionalapplication Ser. No. 60/019,044, filed on May 20, 1996, which is acontinuation-in-part of U.S. Provisional application Ser. No.60/022,948, filed on Aug. 2, 1996.

TECHNICAL FIELD

This invention relates to solenoid valves and fluid control systems foruse in automobiles and other vehicles, one preferred system being asolenoid operated exhaust gas recirculation system for internalcombustion engine.

BACKGROUND OF THE INVENTION

Fluid control valves and fluid flow systems are used throughout anautomobile to control the flow of fluids. Examples of fluid flow systemsinclude (a) air and exhaust gas recirculation (EGR) flow to combustionchambers or cylinders of an internal combustion engine, (b) water flowto control the cooling of an internal combustion engine, and (c)warm/cool air flow to moderate the temperature within the passengercompartment of a vehicle. These fluid flows are typically controlled byfluid control valves, especially solenoid operated valves.

It is now customary to utilize exhaust gas recirculation in the fuelmanagement system of automotive internal combustion engines to reducethe amount of pollutants in the exhaust gas and to improve fuel economy.This is accomplished by capturing a portion of the exhaust gas andcombining the captured exhaust gas with an air/fuel charge for theinternal combustion engine. If the balance between the air, fuel andexhaust gas is such that an ideal stoichiometric mixture is achieved,then maximum power is produced while utilizing a minimum amount of fueland creating a minimum amount of pollutants.

More specifically, incorporating exhaust gas into fuel and air beingburned in combustion chambers is helpful for several reasons. First,pollutants, particularly nitrous oxides (NOx), are more susceptible tobeing produced when temperatures in combustion chambers are high.Exhaust gas has a higher specific heat than air and therefore thepresence of exhaust gas in place of air assists in lowering temperaturesin combustion chambers.

When less than full power from an engine is needed, the combustionchambers do not need a full compliment of air since a reduced amount offuel is typically supplied to them. Accordingly, exhaust gas replaces aportion of the air such that the lesser amounts of fuel and air areagain stoichiometrically balanced. With less air and fuel being burned,the amount of heat produced will be less, again keeping the temperaturein the combustion chambers at a lower level and the amount of pollutantsproduced down.

Further, adding exhaust gas to intake air reduces the amount of work anengine must perform. The exhaust gas is generally at a positive pressurerelative to the intake air. Therefore, the addition of this exhaust gasto intake air reduces the amount of vacuum which must be created bypistons to draw gases into the cylinders.

Care must be taken, however, not to provide an overabundance of exhaustair into the fuel/air/exhaust gas mixture. If too much exhaust gas isintroduced, the engine can run roughly. Accordingly, thefuel/air/exhaust gas mixture introduced into the combustion chambers aretypically controlled to insure that there is an overabundance of fueland air at the expense of not supplying an optimal amount of exhaustgas. Looking to FIG. 1, curves 16A-D represent percentage maximum enginetorque versus engine RPM for a variety of percentage throttle openpositions. Encircled area 17 represents the theoretical portion of thegraph in which exhaust gas should be added to intake air to achieveoptimal gas mileage and reduced pollutants. Encircled area 18 shows amuch reduced portion of encircled area 17 in which conventional enginesare conservatively operated. Area 19, as discussed in more detail below,illustrates the general area of performance of the present invention.Thus, internal combustion engines today are not operated as efficientlyas possible. This is in large part due to the present inability ofsolenoid valve mechanisms to precisely control the introduction ofexhaust gas into an ambient air stream which is then directed to one ormore combustion chambers for burning with fuel.

An exhaust gas recirculation valve of a poppet type is often used toprovide some control of the amount of exhaust gas that is captured andreturned to the internal combustion engine for reburning. In one knownsystem, a mechanically actuated poppet valve has been used in which anelectrical control signal controls a vacuum motor which, in turn,actuates a poppet valve member. However, the response of the vacuummotor-actuated poppet valve member is often too slow to preciselycontrol the input of exhaust gas into intake air even when it iscontrolled by an electronic signal.

Some EGR systems utilize solenoid actuated poppet valve members toprovide a quicker response. See for instance, U.S. Pat. Nos. 4,805,582,4,961,413 and 5,094,218. However, as demonstrated by these patents, thepressure of the exhaust gas in known solenoid actuated EGR valvessupplies forces tending to open the poppet valves members which are heldin the closed position by spring mechanisms. This is a drawback becausethe arrangement requires the use of heavy springs to insure that thepoppet valve members do not lift from their valve seats when thepressure of the exhaust gas is high, such as during engine backfire orunder other engine load conditions.

Furthermore, since the solenoid activated EGR valve systems mustovercome the heavy closing spring forces to open poppet valve members,relatively larger solenoids are required, which result in increased sizeand weight penalties for the systems. These penalties are importantfactors, particularly in automotive applications where weight affectsfuel economy to such an extent that there are continuous and unrelentingongoing efforts today to reduce weight.

Moreover, because springs, poppet valve members, and armatures in knownsystems are large and heavy, significant amounts of current must besupplied to the solenoids to overcome the large spring forces and openthe poppet valve members. This, in turn, increases the load on theelectrical system of the vehicle.

Finally, known EGR valves employing solenoids are often difficult tocontrol. First, because of the relatively heavy or massive componentsused in constructing the EGR valves, the response time for armature andpoppet valve member control can be slow. Also, vibration due to engineoperation and vehicle bounce due to road surface irregularities cancause a massive armature to move independently of the remainder of theEGR valve mounted on a vehicle.

Second, current technology is not well suited to precisely identify theposition of a poppet valve member relative to a valve seat. In thisregard, the position of the poppet valve member determines the quantityof fluid flow through the EGR valve and is therefore significant.Potentiometer based sensors include a metallic conductor affixed to thehousing and at lease one wiper operatively connected to a poppet valvemember and/or an armature. The wiper slides relative to non-movingmetallic conductors within the EGR valve to determine poppet valvemember position. These potentiometer based sensors are susceptible tovehicle vibrations and continuous wear due to cycling of the components.Valves having potentiometer based sensors must be mechanicallycalibrated and are therefore difficult and time-consuming to calibrateduring assembly. Further, their accuracy often significantlydeteriorates over the operating life of an EGR valve.

Another problem with current solenoid actuated EGR valves is that theymay allow air and exhaust gas to leak along the stems of poppet valvemembers and into and out of the EGR valves. This leakage detracts fromthe ability to carefully meter and balance the intakes of ambient airand exhaust gas through the EGR valves.

EGR systems typically contain conduits and orifices of a sufficient sizeto accommodate large amounts of exhaust gas flow. Looking to FIGS. 2Aand 2B, exhaust gas is supplied at a positive pressure P_(P) relative toatmosphere, when expelled during an exhaust stroke from combustionchamber C and into an exhaust manifold. Intake manifolds generally areat a relative negative pressure, P_(N), because an air/exhaust gasmixture is drawn into the combustion chambers C during intake strokes ofpistons P, as shown in FIG. 2B. Accordingly, the flow of exhaust gasfrom the exhaust manifold, through an EGR valve V and into the intakemanifold, is partially limited by the pressure drop between themanifolds. Therefore, the sizes of the conduits and orifices in thesystem must be sufficient to provide a desired maximum exhaust gas flowdue to the available pressure drop in the exhaust and intake manifolds.

Internal combustion engines are also susceptible to clogging due toaccumulation of contaminants and moisture carried by exhaust gases.Exhaust gases often contain heavy particles which can fall or settle outof suspension if fluid flow is too slow, or if the flow passes through asharp bend. As a result, it is common for contaminants to build up inEGR valves or for heavy particles to accumulate within the intakemanifold near the exhaust gas inlet and drop into the first availablecombustion chamber. Therefore, it is advantageous to mix exhaust gas andambient air as homogeneously as possible to maintain the heavy particlesin fluid suspension prior to entry into the combustion chambers.

Moreover, solenoid actuated EGR valves can fail if they overheat.Insulation on wires and coils of a solenoid can deteriorate if thetemperatures in an EGR valve are too high. Therefore, care in designmust be taken to insure that EGR valves are not subjected to excessivelyhigh temperatures.

Another problem encountered with EGR valves is that they are mounted ona wide variety of engines. Hence, different EGR valve configurationsmust be made for each different type of engine. This leads to a largeamount of design work and a need to secure and keep available asignificant inventory of EGR valves with different engine mounts.

Several of the problems with known EGR valves are also present withrespect to known valve mechanisms for controlling water flow to coolengines. Solenoid activated valve mechanisms for these systems often arerelatively large and massive due to the heavy biasing members and forcesnecessary to keep the valves closed. These valve mechanisms addundesirable weight to the vehicles, unnecessarily increasing the load onthe electrical systems of the vehicles, and are difficult to controlwith accuracy and precision. The position of a moveable poppet valvemember and thus the amount of valve opening and fluid flow is alsodifficult to control and measure, and can vary over the life of thevalve mechanism. These problems may also exist with other vehicle andnon-vehicle solenoid controlled valve applications involving fluid flow.

SUMMARY OF THE INVENTION

It is a general object of the present invention to provide an improvedsolenoid activated valve mechanism for use in fluid flow systems,especially in vehicles. These valve mechanisms have particular use inEGR systems and cooling water flow systems, although the invention isnot limited just to use in these systems.

It is a further object of the present invention to provide an exhaustgas recirculation system for an internal combustion engine whichutilizes a highly accurate and responsive solenoid operated EGR valvesuch that the optimal amount of exhaust gas in a fuel/air/exhaust gasmixture can be employed in combustion chambers of an engine thusincreasing the fuel economy of the vehicle and reducing pollutants.

Another object of the present invention is to provide a solenoidoperated valve member that is light and compact and thus particularlyuseful in automotive applications.

It is also an object of the present invention to provide a solenoidoperated EGR valve which utilizes a pressure balanced valve member andarmature such that only a light spring and small solenoid are needed toopen and close the valve member and which requires only a limited amountof current to operate.

Another object is to provide a modular type solenoid subassembly whichcan be assembled, tested and calibrated prior to mounting to one of aplurality of base housings which are specifically configured to mount toa particular engine housing or manifold.

It is yet another object to provide a solenoid activated valve memberwhich uses a more accurate and non-mechanical sensor, to accuratelysense the position of a valve member, and which does not requiremechanical components which can physically wear out.

It is still another object of the present invention to provide aposition sensor in a valve mechanism which can be quickly,inexpensively, and electronically calibrated.

An additional object is to mount a magnet relative to an armature of asolenoid to move with the armature, the magnet being placed outside theflux field of the solenoid valve and adjacent to a Hall effect sensor todetermine displacement of the armature as the magnet reciprocates alongthe Hall effect sensor.

Moreover, it is an additional object of the present invention to providean improved mixing housing for homogeneously mixing two fluid flows,such as inlet air and recirculated exhaust gas in an EGR system.

It is still a further object of the present invention to provide amodular type pressure balanced solenoid operated EGR valve forincorporation into a diesel engine.

A feature of the present invention is the use of a mixing housing in anEGR system which utilizes a venturi effect to increase exhaust gas flowfrom an exhaust manifold to an intake manifold.

These and other objects are met with the embodiments of the presentinvention. Specifically, in accordance with the present invention, aunique solenoid activated fluid flow control valve mechanism isprovided, along with a unique housing for homogeneously mixing two fluidflows. The valve mechanism has a pressure balanced armature and valvemember which allows use of a light return spring and small solenoid sothat the valve mechanism is lighter in weight, smaller and more compactin size, and less expensive to manufacture and operate than conventionalsolenoid operated valve mechanisms. The valve mechanism reduces the loadon the electrical system of the vehicle and can be more preciselyoperated to more accurately control and record the flow of fluidtherethrough. Also, the valve mechanism uses a magnetic flux orelectromagnetic field responsive sensor, such as a Hall effect or aninductance sensor, to accurately sense the position of the valve memberrelative to a valve seat. The sensor has minimal wear and minimalreduction in accuracy over its operating life.

In accordance with one aspect of the invention, the solenoid operatedvalve mechanism preferably has a hollow valve member carried by a hollowarmature of the solenoid so that the force of a fluid on a valve memberand/or armature is evenly balanced when the valve member is in a closedposition preventing fluid flow. The solenoid operated valve mechanismalso has an armature which may be part of an expandable chamber fluidlyconnected to a fluid source (e.g. exhaust gas) when the valve member isclosed so that the pressure of the fluid source produces a forcecomponent assisting in maintaining the valve member in the closedposition. The hollow armature may be piloted on a stem so that thepressure on the valve member is equalized when the valve member isclosed. Preferably, the valve member is also pressure balanced when inan open position.

In an alternative embodiment of the invention, the solenoid operatedvalve mechanism has an expandable mechanism that includes a metallicbellows that provides a spring force and a force component responsive tofluid flow that assists in keeping the valve member in the closedposition while providing a sealed chamber preventing fluid from escapingthe valve mechanism.

The preferred mixing housing for use with the solenoid activated valvemechanism, particularly when used in an EGR system, is more compact insize than conventional intake air-exhaust gas mixing apparatus and morehomogeneously mixes the two fluids. The fluid mixing housing has aninlet channel ideally of diminishing cross-sectional size whichintercepts a portion of a first fluid flow and directs it to a mixingchamber. The mixing chamber also receives a second fluid, such asexhaust gas, and is connected to an outlet channel of preferablyincreasing cross-sectional size. The outlet channel returns the portionof the first flow, which is now homogeneously mixed with the secondfluid flow to the first fluid flow. The first fluid flow induces thesemixed fluids to be drawn out of the outlet channel. A venturi effect iscreated in the mixing chamber which increases the pressure drop from anexhaust gas manifold to the mixing chamber and which enhances gas flowin the system without having to increase the size of a conduit carryingexhaust from the exhaust manifold to the intake manifold.

The unique mixing housing, when used as part of an EGR valve mechanism,reduces contamination buildup along the valve seat due to the passingairstream which keeps the exhaust gas particles in suspension andflushes away settled particles. Cooler air also is used to cool down thevalve member and thereby reduce temperature migration into otherportions of the valve mechanism, such as the solenoid. The housingfurther utilizes venturi effects to create an additional pressure dropin the mixing housing to enhance fluid flow through the mixingmechanism.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the presentinvention will become more apparent from the following description whentaken in conjunction with the accompanying drawings and appended claims.

FIG. 1 is a graph of percentage of maximum engine torque versus enginerevolutions per minute (RPM) for various throttle-open positions, thegraph includes encircled regions showing under what conditions exhaustgas is added to intake air;

FIGS. 2A and B schematically illustrate respective pistons in combustionchambers expelling exhaust gas and drawing in a mixture of intake airand exhaust gas during exhaust and intake strokes, respectively, of anengine to recirculate exhaust gas in a conventional exhaust gasrecirculation system;

FIG. 3 is a schematic view, partially cut away, of an exhaust gasrecirculation system including a pressure balanced solenoid actuatedexhaust gas recirculation (EGR) valve mechanism and a fluid mixinghousing, made in accordance with the present invention;

FIG. 4 is an exploded perspective view of the preferred fluid mixinghousing with an EGR valve mechanism mounted thereon in fluidcommunication with an air intake passageway and a collector;

FIG. 5 is a cross-sectional view taken generally along line 5—5 of FIG.3;

FIG. 6 is an enlarged view of a portion of FIG. 5;

FIGS. 7A-G are cross-sectional views taken from the fluid mixing housingas indicated by lines 7A—7A, 7B—7B, 7C—7C, 7D—7D, 7E—7E, 7F—7F and7G—7G, respectively, in FIG. 5;

FIG. 8 is a cross-sectional view of a second embodiment of a pressurebalanced solenoid actuated valve mechanism in accordance with thepresent invention;

FIG. 9 is a cross-sectional view of a third embodiment of a pressurebalanced solenoid actuated valve mechanism in accordance with thepresent invention;

FIGS. 10A-C are free-body diagrams of balancing forces acting on thevalve members and armatures of the respective valve mechanisms shown inFIGS. 5, 8 and 9, respectively;

FIGS. 11A and B are cross-sectional and bottom views of a fourthembodiment of a pressure balanced solenoid valve mechanism including apreassembled solenoid subassembly mounting to a base housing;

FIGS. 12A-E are graphs indicative of steps used in calibrating a fieldsensor used in the inventive valve mechanisms;

FIG. 13 is a block diagram of a feedback system used to control theposition of a valve member;

FIG. 14 is a schematic view including an inductance sensor which is usedas a field sensor;

FIG. 15 is a schematic view of the present invention in a liquid coolingsystem;

FIG. 16 is a cross-sectional view of a fifth embodiment of a pressurebalanced solenoid actuated valve mechanism in accordance with thepresent invention;

FIG. 17 is a free-body diagram of balancing forces acting on an armatureand magnet holder of the valve mechanism of the fifth embodiment;

FIG. 18A is schematic view of a magnet reciprocating past a Hall effectsensor;

FIG. 19 illustrates that output voltage from a Hall effect sensor islinear with respect to movement of an armature, magnet holder and magnetmounted thereon;

FIG. 20 is a schematic view of a Hall effect sensor passing current to avoltage divider;

FIG. 21 illustrates the effect of using the voltage divider to changethe slope of a voltage output versus armature displacement curve forvoltage output from the arrangement of FIG. 20;

FIG. 22 is a cross-sectional view of another embodiment of a pressurebalanced solenoid actuated valve mechanism in accordance with thepresent invention;

FIG. 23 is an enlarged view of a portion of the valve mechanism of FIG.22 illustrating two positions of the diaphragm in accordance with apreferred embodiment of the present invention;

FIG. 24 is a perspective view of a preferred embodiment solenoidactuated valve mechanism in accordance with the present invention;

FIG. 25 is a side view of the solenoid activated valve mechanism shownin FIG. 24.

FIG. 26 is a cross-sectional view of another embodiment of a valvemechanism in accordance with a preferred embodiment of the presentinvention; and

FIG. 27 is a perspective view of another embodiment of a solenoidactuated valve mechanism in accordance with the present invention.

BEST MODE(S) FOR CARRYING OUT THE INVENTION

As explained in more detail herein, the present invention can be used ina number of different applications particularly involving fluid flowsystems for automobiles and other vehicles. For example, the presentinvention can be used in exhaust gas recirculation (EGR) systems andengine water cooling systems. The present invention can also be used inother comparable or equivalent systems where the benefits and featuresof the invention can be obtained. For illustration purposes, by way ofexample and explanation of the features and benefits of the presentinvention, but not for the purposes of limiting its use or application,the present invention will be explained in particular relative to itsuse in an EGR system. It should be understood that the present inventionis intended for use in all types of engines, including both diesel andnon-diesel engines.

Adding exhaust gas to intake air can be quite beneficial to engineperformance, particularly in the areas of enhanced gas mileage andreduction of nitrous oxide (No_(x)) pollutants. FIG. 1 shows a graph ofcurves 16A-D of the percentage of maximum engine torque versus enginerevolutions per minute (RMP) for a variety of throttle positions. Thethrottle positions are expressed as a percentage of opening, 20%, 50%,80%, and 100% for respective curves 16A-D, which reflect the throttle'sability to limit intake air into the intake manifold of the engine. Asthe throttle opening is increased for a given RPM, the torque producedby the engine increases correspondingly.

As indicated in the background, current EGR valves are relatively heavyand therefore are slow to respond. Further, sensors used to identifyvalve member position, which is determinative of exhaust gas flow, arerelatively inaccurate and are susceptible to losing their accuracy.Consequently, mixing exhaust gas with intake air is conventionally doneon a very conservative basis. Encircled area 18, while not exact, isexemplary, of where on the % maximum torque versus RPM curve, exhaustgas is currently utilized in standard engine designs. Encircled area 17indicates the approximate region where the introduction of exhaust gasinto intake air theoretically can benefit engine performance. Encircledarea 19 illustrates the region where the current invention, withenhanced EGR valve feedback control response and improved sensing ofvalve member position, and hence, improved determination of the exhaustgas quantity to be added to intake air, will ideally operate. Thepresent invention thus provides for improved gas mileage and pollutioncontrol through more accurate exhaust gas metering which allows anengine to operate closer to theoretical limits of performance. Thecomponents which allow for this improved EGR system are described below.

FIG. 3 shows a portion of an internal combustion engine 20. Engine 20includes a fluid mixing housing 22 on which an EGR valve mechanism 24 ismounted, both of which are made in accordance with the presentinvention. Mixing housing 22 receives fresh air from an air cleaner 26and exhaust gas from an exhaust gas recirculation tube 28. The air andexhaust gas are mixed in mixing housing 22 and the exhaust gas/airmixture is introduced into a collector 30 of engine 20. An intakemanifold 31 comprises mixing housing 22 and collector 30.

Collector 30 fluidly connects with one or more engine cylinders 32 (oneshown) which serve as combustion chambers. A piston 40 and connectingrod 42 are disposed in each of the cylinders 32. Power is transferred toa crankshaft (not shown) by piston 40 and connecting rod 42 when afuel/air/exhaust gas mixture is burned in cylinder 32. Intake valve 34and exhaust valve 36 control the flow of gas into and out of cylinder32. Exhaust gas exiting cylinder 32 passes into an exhaust manifold 38.Conduit or tube 28 feeds a portion of the exhaust gas from exhaustmanifold 38 to mixing housing 22.

Piston 40 draws in the exhaust gas/air mixture during an intake strokecreating a negative pressure P_(N) in the intake manifold 31 relative tothe ambient atmospheric air pressure. A positive pressure P_(P),relative to ambient atmospheric air, is established in exhaust manifold38 due to the exhaust gas being forced from cylinder 32 during anexhaust stroke. Accordingly, exhaust gas readily passes from exhaustmanifold 38 through tube 28 to mixing housing 22 which is in fluidcommunication with intake manifold 31.

Other components of engine 20 include an engine controller 50, a massair-flow sensor 52, air cleaner 26, and intake and exhaust valveactuators 54 and 56, respectively, which control intake and exhaustvalves 34 and 36. Also, a throttle 60 for controlling air input isdisposed in an air intake passageway 62 positioned between sensor 52 andmixing housing 22. A fuel injector mechanism 64 controls the flow offuel into cylinder 32. Engine controller 50 receives input data such asengine speed, manifold pressure, temperature, and mass flow anddispatches signals which control the operation of EGR valve mechanism24, throttle 60 and fuel injector mechanism 64, as well as other enginecomponents.

FIG. 4 illustrates the combination of the fluid mixing housing 22, airintake passageway 62 and collector 30, as well as the connectionarrangement between them. Fluid mixing housing 22 has a central bore orpassageway 66 therein with an upstream inlet 67 and a downstream outlet68. Bore 66 extends along a longitudinal axis 69. The air intakepassageway 62 and collector 30 are fastened to housing 22 by mountingplates 70 and 71, respectively. Mounting plate 71 has threaded holes 74,while mounting plate 70 and fluid mixing housing 22 have through holes76 and 80, respectively. Four bolts 81 (only one of which is shown) passthrough holes 76 and 80 and are threadedly received in threaded holes74. In this manner, housing 22 is securely held in position between airpassageway 62 and collector 30.

EGR tube 28 is also connected to housing 22, as described in more detailbelow. EGR tube 28 extends upwardly through passageway/bore 66transverse to axis 69 and is held in position by the two halves ofmixing housing 22.

A cross-sectional view through housing 22, EGR valve mechanism 24 andtube 28 is shown in FIG. 5. Mixing housing 22 is preferably made of anon-magnetic material, preferably plastic, although other non-metallicmaterials such as aluminum may also be used. Valve mechanism 24 includesa solenoid assembly 82 which is securely fastened to housing 22. Valvemechanism 24 operates a moveable valve member 84 to control the exhaustgas flow from tube 28 into a mixing chamber 86 in mixing housing 22.

FIG. 6 shows an enlarged cutaway of the solenoid assembly 82, valvemember 84 and housing 22. An armature 88 of the solenoid assembly 82 isattached to valve member 84. Valve member 84 has a stem member 90 and afrustoconical or funnel shaped valve head 92. Valve head 92 selectivelyopens and closes relative to a valve seat 94 formed on the end of tube28 to open and close communication between EGR tube 28 and mixingchamber 86. The mating configuration between valve head 92 and valveseat 94 is selected to produce a flow profile, such as a linear orparabolic profile, as is well known in valve design.

Referring to FIG. 5, most of the air from air cleaner 26 passes throughcentral bore 66 in housing 22. However, in accordance with the presentinvention, a portion of the incoming air is directed through asubstantially arcuate channel or passageway 95. Passageway 95 has anupstream opening inlet channel 96 and a downstream opening outletchannel 98. A portion of the air flow through housing 22 is captured byinlet channel 96 and passes circumferentially through mixing chamber 86where it is mixed with exhaust gas from EGR tube 28. The exhaust gas/airmixture then passes from mixing chamber 86 to outlet channel 98 wherethe mixture is rejoined with the main air flow traveling through centralbore 66.

The preferred mixing housing for use with the solenoid activated valvemechanism, particularly when used in an EGR system, is more compact insize than conventional intake air-exhaust gas mixing apparatus and morehomogeneously mixes the two fluids. The fluid mixing housing has aninlet channel ideally of diminishing cross-sectional size whichintercepts a portion of a first fluid flow and directs it to a mixingchamber. The mixing chamber also receives a second fluid, such asexhaust gas, and is connected to an outlet channel of preferablyincreasing cross-sectional size. The outlet channel returns the portionof the first flow, which is now homogeneously mixed with the secondfluid flow, to the first fluid flow. The first fluid flow induces thesemixed fluids to be drawn out of the outlet channel. A venturi effect iscreated in the mixing chamber which increases the pressure drop from anexhaust gas manifold to the mixing chamber and which enhances gas flowin the system without having to increase the size of a conduit carryingexhaust from the exhaust manifold to the intake manifold.

The disclosed mixing housing, when used as part of an EGR valvemechanism, reduces contamination build-up along the valve seat due tothe passing airstream of increased velocity which keeps the exhaust gasparticles in suspension and flushes away settled particles. This airstream also acts to cool down the valve member and thereby reducetemperature migration into other portions of the valve mechanism, suchas the solenoid. The housing further utilizes venturi effects to createan additional pressure drop in the mixing housing to enhance fluid flowthrough the mixing mechanism.

Fluid mixing housing 22 includes a counterbore 100 which forms aninternal shoulder 102. The solenoid assembly 82 is positioned in bore100. A bearing plate 104 is seated with a press fit connection into bore100 and guides the reciprocation of stem member 90 by means of a guidebore 106. Bearing plate 104 also has access holes 110 which permit fluidcommunication between mixing chamber 86 and solenoid assembly 82. Mixingchamber 86 is defined generally as the space between bearing plate 104and EGR tube 28 in housing 22.

Solenoid assembly 82 further comprises an annular shaped housing 112 ofmagnetic steel or the like which has an outer wall 114, an annularbottom wall 116 and an inner wall 120. Bottom wall 116 of housing 112 isattached to mixing housing 22 by fasteners 122 (one shown) which arereceived in tapped holes 124 in mixing housing 22.

Solenoid assembly 82 further includes a coil 130 which comprises a spool132 of suitable plastic and a wire 134 of copper or other suitableelectrically conductive material. Wire 134 is wound on a hollow shaft136 of spool 132 between two end plates 140 and 142. Spool 132 fitsradially between outer wall 114 and inner wall 120 of housing 112. Innerwall 120 extends preferably about one-half the length of hollow shaft136.

Solenoid assembly 82 has an annular cover 144 which is screwed into theopen upper end of the housing 112. Annular cover 144 has a dependingannular flange 146 which is concentrically arranged with respect toinner wall 120 of housing 112. Flange 146 extends part way into thespool 132. Cover 144 is made of a magnetic material such as soft iron orthe like so that cover 144 and housing 112 act as a pole piece. Whencover 144 is attached to housing 112, the lower end of depending flange146 is positioned adjacent the upper end of armature 88 and spaced fromthe upper end of the inner wall 120 so that armature 88 is drawn up intothe pole piece when coil 130 is energized.

Armature 88 is made of a magnetic material and is disposed inside coil130 and within inner wall 120. Armature 88 has a hollow cylindrical body150 and a bottom wall 152 which has a threaded bore 154. Hollow valvemember 84 has an upper end which is attached to armature 88 and a flaredlower end forming valve head 92. Valve member 84 may be attached in anysuitable manner to armature 88, such as by being threaded into athreaded bore, as shown in FIGS. 5 and 6. The flared valve head 92 ispositioned and adapted to engage valve seat 94 to produce the desiredflow profile when valve member 84 is opened.

The inner diameters of inner wall 120 and depending flange 146 aresubstantially identical and larger than the outer diameter of armature88 to provide an annular air gap 160 therebetween. Air gap 160 allowsequalization of pressure inside solenoid assembly 82 and mixing chamber86 via access holes 110. This pressure equalization is enhanced byproviding a plurality of longitudinal grooves 162 around the perimeterof the outer surface of cylindrical body 150 of armature 88.

Solenoid assembly 82 further includes a hollow stem 164 that dependsfrom a threaded cap 166 which is screwed into annular cover 144. Thelower end of the hollow stem 164 is closed and is situated inside theupper end of hollow armature 88 with a close sliding fit existingtherebetween. In this manner, hollow armature 88 reciprocates on thestem 164 and forms an expandable mechanism that includes a sealedchamber 168 which is fluidly connected with mixing chamber 86 by way ofan orifice 169 in bottom wall 152 which in turn communicates with hollowvalve member 84. This allows balancing forces created by the exhaust gasto act on the moving combination of valve member 84 and armature 88 aswill be described in greater detail below.

Solenoid assembly 82 also includes a return spring in the form of a coilspring 170 which surrounds stem 164. Spring 170 engages the top ofarmature 88 and acts to force armature 88 downwardly away from threadedcap 166 and toward housing 22.

Engine controller 50 controls the current which is fed to coil 130 ofsolenoid assembly 82 in a programmed manner so that armature 88reciprocates upon hollow stem 164 and moves valve head 92 of valvemember 84 toward and away from valve seat 94. When energized, coil 130pulls armature 88 vertically with respect to the coil 130 against theforce of coil spring 170 and thus pulls valve member 84 away from valveseat 94. This establishes fluid communication between EGR tube 28 andmixing chamber 86 so that the exhaust gas can flow into mixing chamber86 and mix with the air in chamber 86.

When coil 130 is deenergized, valve head 92 of valve member 84 is seatedagainst valve seat 94 by coil spring 170 thus blocking the flow of theexhaust gas past the valve seat 94. In this closed position, the exhaustgas cannot flow into mixing chamber 86. However, the exhaust gascommunicates with sealed chamber 168 of the expandable mechanism via thehollow valve member 84 to pressure balance valve member 84 and armature88 in the closed position.

As seen in FIGS. 5 and 10A, the combination of valve member 84 andarmature 88 has numerous annular surfaces which are pressure responsiveto vertically applied pressure induced forces. These annular surfacesinclude inside and outside funnel surfaces 172 and 174, interiorarmature surface 176, bottom armature surface 180 and top armaturesurface 182.

In the closed position, the exhaust gas pressure acting against annularsurface 176 creates a downward closing force while the exhaust gaspressure acting against the inner surface 172 of valve head 92 createsan upward opening force. A precise pressure balance can be achieved bysizing the horizontal projected areas of surfaces 172 and 176 to produceupward and downward forces that are equal and opposite to each other.Alternatively, it may be desired to slightly pressure bias valve member84 and armature 88 to a closed position in the event return spring 170were to break.

This pressure balancing allows use of a lighter coil spring 170 becausethe spring does not need to counteract exhaust gas pressure inducedforces tending to open valve member 84. The lighter coil spring 170, inturn, reduces the electromotive force which must be produced by solenoidassembly 82 to move armature 88 and open valve member 84 against theforce of spring 170. Since the electromotive force requirement isreduced, a smaller and lighter solenoid assembly can be used.Furthermore, a lower operating current to energize coil 134 can beemployed.

Valve member 84 is also preferably pressure balanced on the vacuum sidein either the closed or open positions. In a closed position, a negativepressure, relative to ambient air pressure, is found in mixing chamber86. The negative pressure acts on outer surface 174 of valve head 92 andproduces an upward valve opening force. However, mixing chamber 86 andthe exterior of armature 88 are also at substantially the same negativepressure due to access holes 110 in bearing plate 104 which establishcommunication between armature 88 and mixing chamber 86. Thus thenegative pressure acting on the bottom annular surface 180 of armature88 produces a valve closing force. At the same time the vacuum pressurein solenoid assembly 82 acting on top annular surface 182 of armature 88produces a valve opening force. A precise negative pressure balance canbe achieved by sizing the areas of surfaces 174, 180 and 182 to producea relatively balanced valve closing force.

FIG. 10A more clearly shows the forces which act to move valve member 84and armature 88 between the open and closed positions. Resultant forcesacting on projected horizontal surfaces due to positive relativepressure are identified by F_(PP) (force positive pressure). Similarly,relative negative forces pulling on projected horizontal surfaces aredesignated with F_(NP) (force negative pressure). The positive forceF_(PP) acting on annular surface 172 balances the positive force F_(PP)acting on annular surface 176. Independently, negative forces F_(NP)acting on surfaces 174 and 182 balance the downward force F_(NP) onannular surface 180. Regardless of the magnitudes of the negative orpositive pressures, armature 88 and valve member 84 will not be inducedto open or close the valve. The small spring force F_(SP) exerteddownwardly by spring 170 on annular surface 182 is sufficient to keepthe valve member 84 closed. Again, only a small electromotive force isneeded to overcome spring force F_(SP) to unseat valve member 84 fromvalve seat 94.

In this regard, if the positive pressure exhaust gas and negativepressure vacuum from mixing chamber 86 are both precisely balanced onvalve member 84 and armature 88, spring 170 only needs to besufficiently strong to keep valve member 84 closed against vibrationsencountered during operation of the vehicle in which the valve mechanism24 is installed. With such a spring, the size and weight of solenoidassembly 82 and/or the operating current requirements can besubstantially reduced.

Valve mechanism 24 also preferably includes a non-contact type fieldsensor 184, such as a Hall effect sensor, shown in FIG. 5, to monitorthe position of the armature 88 and valve member 84. Field sensor 184,which is housed in the upper end of threaded cap 166 by a plastic plug185 or the like detects the magnetic flux density induced by solenoidcoil 130 which changes with the movement of the armature 88 anddetermines the precise position of the armature 88 and valve member 84.This precise position measurement is used to accurately control thestroke of armature 88 and the opening between the valve member 84 andvalve seat 94. Hence, the present invention can be used to combineexhaust gas with fresh air flowing through mixing chamber 86 andintroduce the gas mixture to the intake manifold 31 with greaterprecision than conventional EGR valves. This in turn results in emissionreductions and increased fuel efficiency. Another advantage of the useof the Hall effect field sensor 184 is that the sensor can be easilypackaged inside the solenoid assembly 82 to provide a compact,lightweight integral unit. The calibration of field sensor 184 will bedescribed later with respect to FIGS. 12 and 13.

Referring again to FIG. 5, the details and features of a preferredmixing housing 22 will now be discussed. Housing 22 includes first andsecond half members 200, 202 which are preferably made of a moldedplastic, such as a glass reinforced nylon. However, other materials suchas aluminum may also be used. This choice is partially dependent uponEGR gas temperature. Further, housing 22 may be split in otherdirections rather than laterally as shown.

As described above, first and second half members 200, 202 are providedwith holes 80 for receiving bolts 82. An end portion of EGR tube 28extends into mixing housing 22 and cooperates with EGR valve mechanism24 to selectively control the input of exhaust gas into mixing housing22. First and second half members 200, 202 have respective grooves 204and 206 which clamp about tube 28 at the point where tube 28 entershousing 22. A terminal end portion 210 of the tube 28 is clamped byarcuate seal portions 212, 214 of first and second half members 200,202. Also, arcuate cavities 222 and 224 are formed in housing 22 whichdefine counterbore 100, counterbore 97, and mixing chamber 86.

Inlet channel 96 and outlet channel 98 are formed in respective firstand second half members 200 and 202. The cross-sectional sizes andshapes of channels 96 and 98 along their lengths are shown in FIGS.7A-G. Inlet channel 96 has a circumferentially extending open segment234 (FIG. 5) with inlet opening 235 (FIG. 7A) which opens generallyupstream into the axial flow of the fresh air from air intake passageway62. In contrast, outlet channel 98 has a circumferentially extendingoutlet segment 236 (FIG. 5) with outlet opening 237 (FIG. 7G) whichopens downstream in the direction of air flow toward intake valve 34. Asshown in FIGS. 5, 7C, 7D and 7E, the inlet and outlet channels 96 and 98also have respective closed segments 240 and 242 near mixing chamber 86.

Viewing housing 22 in FIG. 5 as a clock face, and taking into accountthe cross-sections as shown in FIGS. 7A-G, open segments 234 and 236extend clockwise approximately between the 7:30 and 11:30 positions andthe 12:30 and 4:30 positions, respectively. Closed segments 240 and 242,together with mixing chamber 86, extend circumferentially between the11:30 and 12:30 positions.

As an overview, a portion of the air flow from air passageway 66 isintercepted by inlet channel 96 and circumferentially funnelledclockwise to outlet channel 98 where the intercepted air is reunitedwith the main air flow travelling through main bore 66 to collector 30.Exhaust gas from EGR tube 28 is introduced into mixing chamber 86 andmixed with the air captured by inlet channel 96. The mixture of exhaustgas and air is then discharged through outlet channel 98. Thus, arcuatechannel 95 which includes inlet channel 96, mixing chamber 86 and outletchannel 98, serves as a generally arcuate mixing bypass in housing 22.

As explained above, cross-sectional views through inlet and outletchannels 96 and 98 are shown in FIGS. 7A-G. Inlet channel 96 is definedby an inlet flap 250, a downstream portion 252, an outer wall portion254 and an upstream portion 256 (see FIG. 7A). Inlet flap 250 extendsaxially upstream and radially inwardly from downstream portion 252.Upstream portion 256 also includes a tapered wall 257 which extendsradially inwardly. Inlet opening 235 is formed between inlet flap 250and upstream portion 256.

Outlet channel 98 has an outlet flap 262, an upstream portion 264, anouter wall portion 266 and a downstream portion 268 (see FIG. 7G).Outlet flap 262 extends axially downstream and radially inwardly fromupstream portion 264, and upstream portion 264 and downstream portion268 extend radially inwardly from outer wall portion 266 and defineoutlet opening 237 therebetween.

Both inlet and outlet channels 96 and 98 vary in cross-section alongtheir circumferential lengths. In FIG. 7A, inlet opening 235 has amaximum cross-sectional area. As shown in FIGS. 7A and 7B, inlet opening235 decreases in size as inlet channel 96 extends circumferentiallyclockwise toward mixing chamber 86. The cross-sectional area bounded byinlet channel 96 also decreases as inlet channel 96 extendscircumferentially clockwise.

At approximately the 11:30 position and as shown in FIG. 7C, inlet flap250 connects with upstream portion 256 such that inlet channel 96becoming a closed rather than open channel thus defining the transitionbetween open and closed segments 234 and 240. Note that thecross-sectional size of inlet channel 96 is substantially smaller thanthat of outlet channel 98 directly adjacent mixing chamber 86 (as shownby a comparison of FIGS. 7D and 7E). Also, inlet channel 96 narrows incross-section from its beginning to end, as indicated in FIGS. 7B, 7Cand 7D.

Mixing chamber 86 connects closed segment 240 of inlet channel 96 withclosed segment 242 of outlet channel 98. Ideally, the minimalcross-sectional flow area in mixing chamber 86, with valve member 84present, is less than that of inlet channel 96 at section 7D—7D. Closedsegment 242 of outlet channel 98 is shown in FIG. 7E at approximatelythe 12:30 position. As outlet channel 98 continues clockwise, outletflap 262 extends increasingly radially inwardly thereby increasing thesize of outlet opening 237, as sequentially shown in FIGS. 7E-7G. Also,the area bounded by outlet channel 98 increases as outlet channel 98extends circumferentially clockwise.

In operation, air flows downstream from air passageway 62 throughhousing 22 and to collector 30. A portion of the air flow is captured byinlet flap 250 which funnels the captured air circumferentiallyclockwise through inlet channel 96. As the cross-sectional size of inletchannel 96 decreases in the clockwise direction, the pressure decreasesand velocity of the captured air increases at closed segment 240adjacent mixing chamber 86. With the valve member in the open position,the cross-sectional area of the mixing chamber is smaller than thecross-sectional area of the adjacent inlet channel. Thus, air velocityis at a maximum as it passes through the mixing chamber 86. Accordingly,with the valve member 84 open, the high speed of the captured airpassing across tube 28 in mixing chamber 86 creates a first venturieffect which causes exhaust gas to be drawn into mixing chamber 86.

The mixture of exhaust gas and captured air exits the mixing chamber 86into closed segment 242 of outlet channel 98. The exhaust gas/airmixture travels to open segment 236 and escapes downstream throughoutlet opening 237. As outlet channel 98 opens and increases in sizecircumferentially clockwise, the mixture of exhaust gas and captured airdecreases in velocity. The fast flow of the main air stream passingthrough central bore 66 of housing 22 across outlet opening 237 createsa second venturi effect which draws the exhaust gas/air mixture frommixing chamber 86 through outlet channel 98 and back into the main airflow passing into collector 30. The interaction between the air andexhaust gas results in the exhaust gas being thoroughly mixed with theintake air and the particulates in the exhaust gas swirling andremaining in fluid suspension.

The above arrangement and use of mixing housing 22 has numerousadvantages over conventional EGR and other fluid mixing systems. First,housing 22 is compact and lightweight and effectively mixes two separatefluids, e.g. exhaust gas and air, in a compact area. Second, when valvemechanism 24 is open, the low pressure in mixing chamber 86 draws thetwo fluids into mixing chamber 86 and increases the exhaust gas fluidflow through mixing housing 22 as compared to the exhaust gas flow dueonly to the pressure of the exhaust gas. Further, contamination buildupin valve seat 94 of valve member 84 and bearing plate 104 is reduced dueto the high velocity cleansing air stream passing circumferentiallytherealong. Finally, high velocity fluid flow through mixing housing 22cools down valve member 84 and associated stem member 90 which reducesheat transfer into solenoid assembly 82.

The graphs in FIGS. 12A-E relate to the calibration process of the fieldsensor 184. Field sensor 184 in the preferred embodiment is aratiometric linear Hall effect sensor such as models 3506, 3507 or 3508sold under the trademark Allegro by MicroSystems, Inc. of Worcester,Mass. Alternatively, a GMR (Giant Magneto Resistive) sensor can be usedsuch as Model NVS5B100 available from Non-Volatile Electronics, Inc. ofEden Prairie, Minn. As seen in FIG. 12A, field sensor 184 produces anoutput voltage of one-half the input voltage to field sensor 184 in theabsence of any magnetic flux, which in this exemplary case, is 2.5 voltsfor a 5 volt input.

Curve 270 of FIG. 12A represents the output voltage from field sensor184 due to magnetic flux produced as a result of current flowing throughcoil 130. At approximately 0.25 amperes, valve member 84 begins to openovercoming the bias of spring 170. As the current through coil 130increases and as armature 88 moves closer to field sensor 184, thestrength of the magnetic flux field about field sensor 184 increases andaccordingly so does the output voltage produced by field sensor 184.

It is foreseeable that valve member 84 and armature 88 might becomestuck closed or open despite current flowing through coil 130. FIG. 12Bdepicts the output voltage, curve 272, from field sensor 184 due tocurrent flowing through coil 130 over the normal operating current rangewhile valve member 84 is held in a closed position. It is desired thatan output voltage will be produced and sent to the engine controller 50which is indicative of the position valve member 84 and is not dependentupon the current flowing through coil 130.

In an effort to nullify the effect of current flowing through coil 130on the magnetic flux field near field sensor 184, this coil currentinduced voltage output, curve 272, is subtracted from the overallvoltage output curve 270. Preferably, a 1.0 ohm resistor (not shown) isplaced in series with coil 130. By evaluating the voltage across thisresistor, the corresponding current through the resistor and coil 130are determined. Curve 274 in FIG. 12C describes the resistor voltageversus coil current. This output voltage is then amplified, by anauxiliary control circuitry (shown in FIG. 13) to produce an outputvoltage versus current curve 276 having the identical slope to that ofcurve 272 in FIG. 12B. This voltage is then offset by 2.5 volts so thata voltage curve 272′, depicted in FIG. 12D, is produced which isgenerally identical to curve 272 of FIG. 12B. The difference in voltagebetween curves 270 and 272′ is then amplified by control circuit 280 toideally give a 0-5 volt output over the operating current range of thesolenoid assembly 82. This amplified voltage is then calibrated againstdisplacement of valve member 84 using a LVDT (Linear VariableDisplacement Transducer) to produce curve 278 of FIG. 12E.Alternatively, flow through valve assembly 24, at a static pressure,could be calibrated against this output voltage 278 using a flow meter.

Control circuitry 280, which is schematically shown in FIG. 13, ismounted on a circuit board (not shown) in the vehicle. The outputvoltage from field sensor 184 is fed to control circuitry 280. Likewise,the voltage from across the resistor is communicated to the controlcircuitry 280 where this voltage is amplified and offset, as depicted inFIG. 12D. The differences in these voltages is amplified, FIG. 12E, toproduce a voltage output which is communicated to engine controller 50.This voltage is representative of the position of valve member 84.Vehicle engine controller 50 then controls the current in solenoidassembly 82 to control armature 88 and the admittance of exhaust gasinto mixing housing 22. Conventional electronic elements are used alongwith laser trimming of resistors on the control circuitry 280 tocalibrate control circuitry 280. This laser trimming and calibrationoccurs during the assembly of valve mechanism 24. Further, thiscalibration procedure accommodates errors due to, including, but notlimited to, tolerancing of components such as housing 112, valve member84, etc.

As an alternative to using a Hall effect field sensor, an induction typefield sensor 282 may be used in place of field sensor 184. Inductancetype position sensors are conventionally known. Referring to FIG. 14,inductance sensor 282 has first and second coils 284 and 286 mounted ona backing plate 288. Backing plate 288 is mounted within cap 166 inplace of field sensor 184. The upper end of armature 88 is generallyaligned with first coil 284 when valve member 84 is in a closedposition. Since armature 88 is spaced away from second coil 286, littleinductance is created in second coil 286. When coil 130 is energized,however, armature 88 and valve member 84 are moved toward cap 166 andfield sensor 282. First coil 284 induces a current in armature 88 which,in turn, induces a current in second coil 286. The current, orfrequency, in second coil 286 is indicative of the relative displacementof armature 88 from its closed position.

Conditioning circuitry is again used to condition the voltage outputfrom inductance sensor 282 against either displacement or flow toproduce a conditioned output voltage. This output voltage may beconditioned to match an engine manufacturer's voltage output versusvalve member displacement or flow specification. Inductance sensor 282and conditioning circuitry are then placed in communication with enginecontroller 50.

FIG. 8 shows another embodiment of an exhaust gas recirculation valvemechanism 300 or fluid flow valve in accordance with the presentinvention. In this embodiment, a metallic bellows 302 is used to bias anarmature 304 to a closed position. The metallic bellows 302 is also partof an “expandable” mechanism that includes an expandable sealed chamber306 which is used to balance the exhaust gas pressure forces acting onarmature 304 and a valve member 310.

More specifically, EGR valve mechanism 300 comprises a valve body 312rather than utilizing fluid mixing housing 22 of the first embodiment. Asolenoid assembly 314 is mounted on valve body 312 for operating themoveable valve member 310 and controlling the flow through valve body312. However, it will be appreciated by those skilled in the art thatsolenoid assembly 314 could readily be adapted to work in conjunctionwith mixing housing 22.

Valve body 312 comprises an inlet passage 316 and outlet passage 317which communicate with a central chamber 318 inside valve body 312.Inlet passage 316 includes an opening 320 and a valve seat 322. Valvemember 310 engages valve seat 322 to block flow through inlet passage316 into central chamber 318. Upon energizing solenoid assembly 314,valve member 310 is moved away from valve seat 322 to allow fluid toflow through opening 320 and into central chamber 318.

A bearing member 324 is seated in an enlarged upper portion of valvebody 312. Bearing member 324 guides reciprocation of valve member 310 bymeans of a central bore 326. Central bore 326 has longitudinal grooves328 to allow fluid communication between central chamber 318 andsolenoid assembly 314. Central bore 326 has longitudinal grooves 328 toallow fluid communication between central chamber 318 and solenoidassembly 314. Bearing member 324 is clamped in place when solenoidassembly 314 is attached to valve body 312 by fasteners 330, only one ofwhich is shown.

Solenoid assembly 314 comprises a cup shaped housing 332 which has anannular bottom wall 334 and an integral cylindrical inner wall 336 ofcircular shape. A coil 340 is disposed in housing 332. An annular cover342 is screwed into the open upper end of housing 332. Annular cover 342has a depending annular flange 344 which is concentrically arranged withinner wall 336. Depending flange 344 extends part way into the coil 340and has an outer conical surface to facilitate assembly. Cover 342 ismade of a magnetic material such as soft iron or the like so that cover342 and depending flange 344 act as a pole piece.

Solenoid assembly 314 further comprises armature 304 made of a magneticmaterial and is disposed inside inner wall 336 of the housing 332.Armature 304 has a hollow cylindrical body 346 with a central bore 350and two counterbores 352 and 354. Valve member 310 includes a hollowtube 356 which has a cylindrical upper end 358 and an enlarged valvehead 360 at its lower end. The cylindrical upper end 358 is pressed intothe inner counterbore 352 of armature 304 to securely attach valvemember 310 to armature 304. The enlarged valve head 360 engages valveseat 322 to close valve mechanism 300.

Solenoid assembly 314 has an expandable mechanism which includesmetallic bellows 302 which is disposed in housing 332 so that one endsealingly engages a threaded cap 362 which is screwed onto housing 332over the annular cover 342. The lower end of the bellows 302 sealinglyengages the upper end of the hollow armature 304. In this mannermetallic bellows 302 forms an expandable sealed chamber 306 for theexpandable mechanism which is fluidly connected with inlet passage 316of valve body 312 via the bore of armature 304 and hollow valve member310. Metallic bellows 302 also acts as a return spring which biasesarmature 304 away from cover 362 toward valve body 312.

Valve mechanism 300, as shown in FIG. 8, is incorporated into an exhaustgas recovery system of the type shown in FIG. 3 by connecting outletpassage 317 to collector 30 with valve body 312 replacing fluid mixinghousing 22. Valve body 312 is threadedly attached to exhaust manifold 38by way of an exhaust conduit (not shown). Threads 363 are formed onvalve body 312 so that valve mechanism 300 may be attached to theexhaust conduit. When installed, solenoid assembly 314 is electricallyconnected to engine controller 50 in a manner similar to thatillustrated schematically in FIG. 3.

Engine controller 50 controls the current fed to coil 340 of solenoidassembly 314 in a programmed manner so that the armature 304reciprocates in the housing 332 moving valve member 310 toward and awayfrom valve seat 322. When energized, coil 340 pulls armature 304 furtherup into coil 340 against the force of collapsing metallic bellows 302which moves valve head 360 of valve member 310 away from valve seat 322.This establishes communication from inlet passage 316 to the centralchamber 318 so that exhaust gases can flow through valve mechanism 300and back into intake manifold 31.

When coil 340 is deenergized, valve head 360 of the hollow valve member310 seats against valve seat 322 by the spring action of the expandingmetallic bellows 302 thus blocking the flow of the exhaust gas pastvalve seat 322. In this closed position, the exhaust gas cannot flowinto central chamber 318. However, the exhaust gas communicates withexpandable chamber 306 inside metallic bellows 302 via the hollow valvemember 310 and the bore of the armature 304 to pressure balance valvemember 310 and armature 346 in the closed position.

A free body diagram of armature 304 and valve member 310 is shown inFIG. 10B. In the closed position, exhaust gas pressure acting against anannular top surface 364 of armature 304 creates a downward closing forcewhile the exhaust gas pressure acting against an annular surface 366 onthe underside of valve head 360 creates an upward opening force. Aprecise pressure balance can be achieved by sizing the areas of surfaces364 and 366 to produce a downward closing force F_(PP) and an upwardopening force F_(PP) that are equal and opposite.

Valve member 310 is also preferably pressure balanced on the vacuum ornegative pressure side. Vacuum or negative relative pressure “pulls” onupper annular surface 370 of valve head 360. In opposition, a downwardforce “pulls” on projected horizontal surfaces 372 and 374 of armature304. By equating the total horizontal projected area of surfaces 372 and374 with the projected area of surface 370, EGR valve mechanism 300 isgenerally pressure insensitive to changes in the relative negativepressure in intake manifold 31. Although not shown, it should beappreciated that position or field sensors as described elsewhere inthis specification can also be used with this embodiment.

Pressure balancing in accordance with the present invention allows useof a light spring and a smaller and lighter solenoid assembly and/or alow operating current for solenoid assembly 314. Metallic bellows 302not only provides an adequate spring force for closing the valve member310, but forms part of the expandable mechanism which provides apressure balance when the EGR valve mechanism 300 is closed.

FIG. 9 shows another embodiment of a fluid flow valve mechanism 400 inaccordance with the present invention. Valve mechanism 400 includes ametallic bellow 402 which is used to bias an armature 404 to a closedposition as well as provide part of an expandable mechanism which isused to balance a valve member 406. Valve member 406 has a stem 407 anda valve head 408. In this arrangement, metallic bellow 402 is sealed byan end plate 410 and is disposed in a casing 412 to provide anexpandable mechanism which pressure balances valve member 406 in boththe open and closed positions.

More specifically, the valve mechanism 400 comprises a self-containedvalve assembly 414 and a solenoid assembly 416. Solenoid assembly 416 isattached to valve assembly 414 for operating moveable valve member 406which is contained in a valve body 420 so as to control flow of exhaustgas through valve mechanism 400 when it is used as an EGR valve.

Valve body 420 comprises an inlet passage 422 and an outlet passage 424.A central chamber 426 is defined in valve body 420 outside casing 412.Casing 412 forms part of an expandable chamber 427. An opening 428 incasing 412 fluidly connects inlet passage 422 with expandable chamber427. When valve member 406 is opened, exhaust gas can pass from inletpassage 422 through expandable chamber 427 to central chamber 426 andout outlet passage 424.

The opposite end walls of casing 412 have coaxially aligned openings432, 434 and a valve seat 436. Valve head 408 engages valve seat 436 toblock flow through the lower opening 434 in casing 412 to centralchamber 424. Moving valve head 408 away from valve seat 436, that is,away from the position shown in FIG. 9, allows flow from inlet passage422 through lower opening 434 in casing 412, into central chamber 424,and out of outlet passage 424.

Stem 407 of valve member 406 is solid and has its opposite ends slidablydisposed in sleeve bearings supported in the opposite end walls of valvebody 420 so that valve member 406 and stem 407 reciprocate in valve body420 along the axis of the aligned openings in the end walls of thecasing 412. The metallic bellow 402 is disposed in casing 412 and has anopen upper end that is sealingly mounted in the upper opening 432 ofcasing 412. The lower end of the metallic bellow 402 is sealed by endplate 410 to form sealed expandable chamber 427 inside casing 412 whichis in communication with inlet passage 422. End plate 410 is attached tostem 407 so that the bellow 402 holds valve member 406 in the closedposition, as shown in FIG. 9, when solenoid assembly 416 is deenergized.

Solenoid assembly 416 comprises a cup shaped housing 446 that has anannular bottom wall 450 which supports a hollow pole piece 452 ofcircular shape. Coil 454 is disposed in housing 446 and is secured tohollow pole piece 452.

An annular bearing plate 456 is embedded in an annular plastic cover 460which is molded onto the open upper end of housing 446. Armature 404 ismade of a magnetic material and is slidably disposed in the alignedbores of the annular bearing plate 456 and plastic cover 460 with itslower end projecting into coil 454. Armature 404 has a hollow bodyincluding a bore 465 which receives a push rod 466 which has an upperthreaded end that is screwed into a threaded upper end 468 of armature404. Push rod 466 extends through the hollow pole piece 452 and engagesthe top of the solid stem 407 of valve member 406. Solenoid assembly 416further includes a cap 470 which fits onto an annular flange of plasticcover 460 to protect the projecting upper end of armature 404.

Valve mechanism 400 is incorporated in an exhaust gas recovery system byconnecting it into a feed back circuit similar to that shown in FIG. 3.In this manner, inlet passage 422 communicates with the exhaust manifold38 and outlet passage 424 communicates with intake manifold 31. Wheninstalled, solenoid assembly 416 is connected to an engine controller,such as controller 50 as illustrated schematically in FIG. 3.

Engine controller 50 controls the current to coil 454 of solenoidassembly 416 in a programmed manner so that armature 404 reciprocates inhousing 446 axially moving valve member 406 toward and away from thevalve seat 436 via push rod 466 and solid stem 440. When energized, coil454 pulls armature 404 toward valve body 420 against the force of anexpanding metallic bellows 402 moving valve member 406 and valve head408 away from valve seat 436. This establishes communication from thechamber 444 of the expandable mechanism to the central chamber 424 sothat exhaust gas flows from inlet passage 422 through the valvemechanism 400 and into intake manifold 31.

When coil 454 is deenergized, valve head 408 of valve member 406 isseated against valve seat 436 by the spring action of the contractingmetallic bellows 402 thus blocking the flow of the exhaust gas pastvalve seat 436. In this closed position, the exhaust gas cannot flowinto the central chamber 424. The exhaust gas in chamber 427 acts on endplate 410 of the metallic bellows 402 as well as valve head 408 of valvemember 406 producing pressure forces that act in opposite directions.These pressure forces can be balanced precisely by sizing an insidesurface area 474 of end plate 410 and the inside surface area 476 ofvalve head 408 so as to produce equal and opposite pressure forcesacting on valve member 406.

Moreover, the vacuum side of EGR valve mechanism 400 can also bebalanced precisely by properly sizing outside surface area 480 of endplate 410 and outside surface area 482 of valve head 408. Accordingly,equal and opposite vacuum pressure forces act on the valve member 406when valve mechanism 400 is closed. Thus metallic bellows 402 not onlyprovides an adequate spring force for closing valve member 406, but alsoforms part of the expandable mechanism that provides a pressure forcebalance and an exhaust pressure force balance when the valve mechanism400 is closed.

FIG. 10C illustrates the balanced forces on valve member 406 due topositive and negative relative pressures exerted on projected horizontalsurfaces when valve mechanism 400 is closed. Negative pressure forcesF_(NP) pull downwardly on valve head 408 and upwardly on end plate 410of bellows 402. Exhaust gas forces, or relative positive pressure forcesF_(PP), act on valve head 408 and end plate 410. By equating theprojected horizontal surfaces of end plate 410 and valve head 408, valvemechanism 400 is relative insensitive to changes in exhaust gas orintake manifold pressures. The upward spring force F_(SP) should besufficiently large to keep valve head 408 seated against vibrationrelated forces.

FIGS. 11A and 11B show a fourth embodiment of a pressure balancedsolenoid actuated valve mechanism 500 made in accordance with thepresent invention. Solenoid valve mechanism 500 is pressure balanced ina manner similar to that described above with respect to valve mechanism24.

Solenoid valve mechanism 500 comprises a base housing 502 to which asolenoid subassembly 504 is mounted. Subassembly 504 is preferablyconstructed, calibrated and tested prior to being mounted to basehousing 502. The specific design of base housing 502 is adapted to meetthe mating or mounting requirements of a particular engine. Therefore,only base housing 502 needs to be changed in order to mount solenoidsubassembly 504 to a wide variety of engines. Alternatively, if asuitable mounting surface is provided on an engine, solenoid subassembly504 can be directly mounted to the engine eliminating the need for basehousing 502.

Solenoid subassembly 504 comprises a coil 506 held within a plasticbobbin 508. The combination of coil 506 and bobbin 508 is retainedwithin an inner housing 510 which is L-shaped in cross-section having aninner wall 511 and a base wall 512. An outer housing 514 partiallysurrounds bobbin 508 and inner housing 510. Outer housing 514 has adownwardly depending annular portion 516 which extends downwardly towardinner wall 511 of inner housing 510. An inner sleeve 518, with a plasticcap 519 disposed in the top thereof, mounts to outer housing 514adjacent downwardly depending portion 516. An armature 520 has a valvemember 522 attached to its lower end. The inner surface of armature 520is piloted upon sleeve 518. A spring 523 biases armature 520 and valvemember 522 downwardly away from cap 519.

A stamped metal insert 524 has a radially extending top flange 526captured between base wall 512 of inner housing 510 and a radiallyinwardly extending retaining flange 530 of outer housing 512. Insert 524further has a shoulder 532 in which a bearing plate 534 is mounted.Bearing plate 534 has access holes 536 extending therethrough to providecommunication between an internal chamber 538, in which valve member 522reciprocates, and an annular space 539 defined between armature 520 andinner housing 510. Insert 524 further has a radially inwardly taperedwall 542 which serves as a valve seat. Finally, insert 524 has anannular terminal portion 544. Valve member 522 has a hollow stem 546attached to armature 520 and a valve head 548 which seats againsttapered wall 542.

Base housing 502 comprises an inlet opening 550 and an outlet opening552 which is in communication with internal chamber 538. The innersurface of base housing 502 is configured to conform to the outersurface of insert 524 and provide support thereto.

In assembly, valve member 522 is placed through bearing plate 534 andaffixed to armature 520. Bearing plate 534 is seated within shoulder 532of insert 524. Inner housing 510 is positioned concentrically aboveinsert 524. Next, bobbin 508 and coil 506 are placed radially aboutinner housing 510. Outer housing 514 is placed over bobbin 508 and topflange 526 of insert 524. As indicated in FIG. 11B, a pair of retainingflanges 528 on outer housing 514 are crimped to secure top flange 526 ofinsert 524 between retaining flange 528 and base wall 512 of innerhousing 510. Next, spring 523 is placed above armature 520 and sleeve518 is placed inside armature 520 capturing spring 523 between armature520 and sleeve 518. Plastic cap 519 supports a field sensor 546, such asa magnetic flux or inductance field sensor. At this point, solenoidsubassembly 504 is assembled and ready to be mated to base housing 502.

Field effect sensor 546 is then calibrated as described previously withrespect to the field sensor 184. Before subassembly 504 is crimped oraffixed to base housing 502, valve assembly 500 is calibrated. Thecalibration process requires energizing coil 506 to the maximum requiredstroke or flow. The test directly measures the flow or stroke with aLVDT (linear variable displacement transducer) or a flow meter. Then,the current to coil 506 is decreased to no stroke or flow. Concurrently,the correlation and calculation of the necessary offsets and/or slopesdepending on the position sensor option, such as displacement or flow,are determined. Thereafter, the appropriate resistors are laser trimmedin order to obtain a desired voltage output vs. stroke (or flow)relationship. It is obvious that the other embodiments of the valveassemblies described in detail above and below can be similarlycalibrated.

The control circuitry is then potted or sealed in order to protectcritical electronic components from water, contamination, etc. Thisprocess minimizes stack up and manufacturing inconsistencies. It alsoallows for relaxed tolerances on components, resulting in lower cost.Lastly, the calibration helps customize output curves from the controlcircuitry 280 for each separate customer and at the same time, providesfinal test for each component before assembly to base housing 502.Preferably, all calibrations will be accomplished by laser trimming ofresistors on the circuit board. Ideally, the circuit board is mountedadjacent the engine controller SO away from excessive engine heat.

After calibration, subassembly 504 is then mounted to base housing 502by crimping four retaining flanges 552 on outer housing 512, as seen inFIG. 11B, to capture base housing 502 between retaining flanges 552 andtop flange 526 of base insert 524. An advantage of this particularassembly procedure is that subassembly 504 can be calibrated and testedwithout base housing 502 being in place. Further, once subassembly 504is calibrated, any one of a number of different configurations of basehousings 502 can be utilized as long as it conforms to be crimped tosolenoid assembly 504. This allows different base housings 502, whichare compatible to different manufactures specifications, to be used withone generally identical subassembly 504. Alternatively, subassembly 504may be directly crimped to a housing or mount on an engine therebydispensing with the required base housing.

The advantages of the above-described valve mechanisms 24, 300, 400 and500 are not restricted to use only as EGR valves in vehicle engines. Thepressure balance solenoid actuated valves may be used for other fluidcontrol applications. For example, in another embodiment, the presentinvention is incorporated into a vehicle cooling system 600, as shownschematically in FIG. 15. The cooling system 600 includes a pressurebalanced solenoid actuated valve mechanism 602, a radiator 604, anengine block 606 and a water pump 610. As the vehicle is operating, heatis transferred from the engine block 606 into water circulatingtherethrough. The water is pumped by water pump 610 through solenoidvalve mechanism 602 to a radiator 604. Radiator 604, a conventionalradiator, is used to release heat from the water to the surroundingatmosphere thereby reducing the temperature of the water flowing throughthe cooling system 600. Water from radiator 604 is returned to coolengine block 606 as needed.

In this embodiment, a block temperature sensor 612 is used to check thetemperature of engine block 606. The temperature is sensed bytemperature sensor 612 and that information is relayed to an enginecontrol unit 614. Alternatively, engine control unit 614 can use a watertemperature sensor 616 rather than the engine block sensor 612.

If the temperature is too low, a signal is sent from engine control unit614 to the solenoid valve 602. In such a situation, the current tosolenoid valve 602 would be limited thereby placing solenoid valve 602in a closed position. Thus, heat will remain in the engine block 606 andnot be carried away by the water to radiator 604.

When the temperature in engine block 606 has reached to a predeterminedlevel, the control unit 614 will send a signal energizing solenoid valve602. Solenoid valve 602 will then be increasingly opened to achieve thedesired flow rate. Water flowing through radiator 604 will release heatand return water to engine block 606 at a reduced temperature.

Using solenoid valve mechanism 602, which is preferably made inaccordance with one of the previously described embodiments of solenoidvalve 24, 300 or 400 or 500, will allow cooling system 600 to enjoy thebenefits provided by the pressure balanced solenoid valve mechanisms ofthe present invention. In particular, because the valve mechanisms arepressure balanced, relatively small springs can be used to keep thesolenoid valves open or closed, depending upon their design, when thesolenoid valve is not energized. When solenoid valve mechanism 602 isenergized, only a relatively small current needs to be used to move thearmature and valve member because solenoid valve mechanism 602 does nothave to overcome or withstand internal pressures of the water flowingtherethrough. Also, solenoid valve mechanism 602 can enjoy the benefitof enhanced controllability of a valve member therein due to thesensitive displacement readings provided by field sensors such as a Halleffect sensor or an inductance sensor in accordance with the presentinvention. Further, these sensors are unlikely to wear out since theyhave no mechanical moving parts. Moreover, they are easily calibratedduring manufacture of the valve assembly and are relatively resistant tobecoming uncalibrated. Another advantage of these valve mechanisms isthat the solenoid assemblies can be reduced in weight making thesolenoid valve mechanisms more economical to manufacture and, at thesame time, lowering the overall weight of the vehicle.

FIG. 16 shows a fifth embodiment of a pressure balanced solenoidactuated valve mechanism 700 made in accordance with the presentinvention. Solenoid valve mechanism 700 comprises a base housing 702 towhich a solenoid subassembly 704 is mounted. Subassembly 704 ispreferably constructed, calibrated and tested prior to being mounted tobase housing 702. The specific design of base housing 702, like basehousing 502 of valve mechanism 500, is adapted to meet the mating ormounting requirements of a particular engine. Consequently, solenoidsubassembly 704 may be used with a wide variety of base housings.

Solenoid subassembly 704 has a coil 706 held within a plastic bobbin708. The combination of coil 706 and bobbin 708 is retained within aninner housing 710 which is L-shaped in cross-section having an innerwall 711 and a base wall 712. An outer housing 714 partially surroundsbobbin 708 and inner housing 710. Outer housing 714 has a downwardlydepending annular portion 716 which extends toward inner wall 711 ofinner housing 710. Inner and outer housings 710 and 714 cooperate toform an annular pole piece. An inner sleeve 718 has a first annularportion 720 with a closed end 721, a second larger diameter annularportion 722 and a radially outwardly extending flange 724. A radiallyextending step 726 is formed between first and second annular portions722 and 724. Flange 724 of inner sleeve 718 is captured between innerhousing 710 and base housing 702 when valve mechanism 700 is completelyassembled.

An armature 730, a magnet holder 732 and a magnet 734 reciprocate withininner sleeve 718 and base housing 702. Armature 730 is hollow having astepped inner bore 731 with a step 733. Magnet holder 732 has adisc-like outwardly extending flange 736, a magnet recess 738 at itsupper end in which magnet 734 is held, a cavity 739 formed in the lowerportion of magnet holder 732 and a pair of access openings 740 providingfluid communication between inner sleeve 718 and cavity 739. A cap 741covers magnet recess 738. The exterior surface of magnet holder 732 isfluted in the axial or longitudinal direction to allow exhaust gas tofreely pass between magnet holder 732 and the first annular portion 720of inner sleeve 711. Alternatively, inner sleeve 718 may be oversizedrelative to the outer diameter of magnet holder 732 to accommodate fluidflow. Magnet 734 has north and south poles N and S, respectively. In thepreferred embodiment, magnet 734 is a Samarium Cobalt (SmCo) magnet.Armature 730 is affixed to magnet holder 732 with flange 736 bearingupon the upper end of armature 732. A spring 742 is disposed betweenstep 726 of inner sleeve 718 and flange 736 of magnet holder 732 biasingarmature 730 and magnet holder 732 away from step 726 and armature 730of valve assembly 700 closed.

A cover 744 affixes over outer housing 714. A Hall effect sensor 746 ismounted to a circuit board 747 and adjacent to magnet 734. The north andsouth poles N and S reciprocate along Hall effect sensor 746 during theoperation of valve mechanism 700, as will be described in greater detailbelow. Also shown in FIG. 16 are a pair of electrical terminals 748which communicate with engine controller 50. In actuality, there arefive terminals, a lead and ground for coil 706 and three leads to Halleffect sensor 746. A connector housing 750 is formed in cover 744 toaccommodate a connector (not shown) which plugs into cover 744 andelectrically connects with terminals 748.

Base housing 702 has an exhaust gas inlet opening 752 and an outletopening 754 formed therein. A pair of mounting ears 756 provide forattachment to an engine. Base housing 702 has an inner bore 760 with afirst step 762 and a radially inwardly extending flange 764. A bearingcollar 766 is held on first step 762 and serves as a guide for armature730. A seat ring 768 rests upon flange 764 and is generally triangularin cross-section. A lower end 770 of armature 730 has a seal surface 772which seals against seat ring 768 to control the flow of exhaust gasthrough inlet opening 752 of valve mechanism 700.

A free body diagram of vertical forces due to exhaust gas pressureacting on armature 730 and magnet holder 732 is shown in FIG. 17. ForcesF_(PP) act upwardly upon seal surface 772 and intermediate step 733 ofarmature 730, and on lower end 784 and the inner horizontal surface ofcavity 739 of magnet holder 732. Exhaust gas pressure acts downwardly onflange 736 and cap 741 of magnet holder 732. Access openings 740 andflutes on the exterior of magnet holder 732 allow exhaust gas to readilyreach flange 736 and cap 741 which are disposed within inner sleeve 718.The horizontal areas upon which the upward and downward forces act aregenerally equal in size. Consequently, as with the valve mechanismsdescribed in the previous embodiments, valve mechanism 700 is generallypressure balanced and spring 742 can be of minimal size.

As schematically shown in FIG. 18, magnet 734 slides axially along Halleffect sensor 746 with the south pole S passing adjacent thereto whenarmature 730 is generally in a closed position and the north pole Npassing thereby when armature 730 is near its full open position. Thenorth pole N creates a positive flux while the south pole S produces anopposite or negative flux in the region surrounding Hall effect sensor746. Hall effect sensor 746, as seen in FIG. 16, is positioned abovecoil 706 and inner and outer housings 710 and 714. Consequently, themagnetic flux produced due to electrical current running through coil706 is negligible as compared to the flux produced by adjacent magnet734.

Ideally, the voltage output from Hall effect sensor 746 varies generallybetween 0.5 and 4.5 volts with 2.5 volts being the output when no fluxis sensed or when positive and negative fluxes are equal and balance oneanother out. A positive flux sensed by Hall effect sensor 746 providesan output greater than 2.5 volts while a negative flux decreases thevoltage output from Hall effect sensor 746 to less than 2.5 volts. TheHall effect sensor 746 output voltage reflects the difference inmagnetic flux between poles of magnet 734 which is linear as indicatedin FIG. 19.

Hall effect sensor 746 is calibrated to produce a voltage output relatedlinearly to the stroke or displacement of armature 730. Subassembly 704is mounted to a test stand including a LDVT (Linear VariableDisplacement Transducer). The LDVT is used to determine the position ofarmature 730 relative to a seat on the test stand similar to that foundon a base housing 702.

Referring to FIG. 20, output from Hall effect sensor 746 is fed to avoltage divider 782 producing a conditioned output voltage which isrecorded versus the displacement δ determined by the LDVT. Initially,with the armature 730 closed and the south pole S adjacent Hall effectsensor 746, a negative flux field is sensed by Hall effect sensor 746.Accordingly, an output voltage, i.e., 0.5 volts is output from voltagedivider 782. Current in coil 706 is then increased until armature 730 issubstantially near its maximum open position. The corresponding voltageoutput from voltage divider 782 is recorded against the sensed armaturedisplacement δ. Curve 784 in FIG. 21 is an extrapolation between thesetwo test values.

The variation in the flux field along magnet 734 is generally linear.Consequently, the voltage output from Hall effect sensor 746 over thestroke δ of armature 730 is also linear. It is desirable to calibratevalve mechanism 700 so that a predetermined slope m or volts/per unitdisplacement is established for valve assembly 700. Because the strengthof magnets used and the tolerancing between components of valveassemblies 700 vary from valve mechanism 700 to valve mechanism 700,output from Hall effect sensor 746 is conditioned by voltage divider 782to establish the desired slope m for the valve mechanism 700.Consequently, displacement of an armature 730 will be proportional, bythe factor or slope m, to the corresponding change in voltage outputfrom voltage divider 782 as a result of movement of armature 730.

The voltage divider 782, although not shown, is preferably mounted oncircuit board 747. Placing circuit board 747 and components thereon awayfrom coil 708 and isolated from exhaust gas within valve assembly 700enhances the life and reliability of the control circuitry on circuitboard 747.

As seen in FIG. 21, line 784 represents the voltage output versusdisplacement curve prior to voltage divider 782 being adjusted. Forexample, a predetermined or desired value of slope m₁ may be chosen tobe equal 1.0 volt/mm. Initially, the slope m₀ will be greater than 1.0volt/mm. Voltage divider 782 is adjusted, preferably through lasertrimming of a resistor R3, until m₁=1.0 volts/mm. Curve 786 has aconditioned slope of m₁, reduced from the unconditioned slope of m₀ ofcurve 784, which corresponds to the output from the untrimmed voltagedivider 782. Of course, other values of m₁ could also be used as long asengine controller 50 is programmed with the correct value of m₁.

Similarly, all other valve assemblies 700 manufactured should have acalibration or slope of predetermined value m₁. This allows any of thevalve assemblies 700 to be mounted to an engine and connected to aengine controller 50. The displacement of an armature 730 can then bedetermined by multiplying the change in voltage output ΔV by the inverseof the slope 1/m₁.

δ=1/m·ΔV where:

δ=displacement;

m=slope or calibration factor; and

ΔV=voltage−baseline voltage.

After valve assembly 700 has been operating in a vehicle for a longperiod of time, possibly years, contamination build-up may occur betweenthe seats on armature 730 and seat ring 768. Consequently, armature 730will not seat directly against seat ring 768 as was the case when valveassembly 700 was first manufactured. To accommodate this build-up, eachtime an engine starts, engine controller 50 takes a baseline reading ofvoltage output from voltage divider 784 when armature 730 is closed.With armature 730 seating upon the build-up, armature 730 will seathigher and the initial output from valve assembly 700 will be slightlygreater than if the build-up were not present. However, the calibrationfactor or slope m₁ (volts/mm) of valve assembly 700 will remainconstant. Curve 788 indicates that while the baseline voltage hasincreased due to the contamination, the slope m₁ will remain constant.Consequently, engine controller 50 can calculate the displacement fromthe seated position of armature 730 to any other position simply bymultiplying the change in voltage ΔV from the baseline voltage by linearfactor 1/m.

Again, the advantages to this type of Hall effect sensing technique isthat there is no moving parts, other than the armature, magnet holderand magnet, and it is entirely non-contact. The system can be calibratedwhich helps make the valve mechanisms more manufacturable, and allowsfor tighter specifications. Calibration also allows for the use ofdifferent housing or casting styles.

Turning now to FIGS. 22 and 23 which illustrate another embodiment of anEGR valve mechanism 800 in accordance with the present invention. Thevalve mechanism 800 includes a sensor housing 801, a solenoid housing802, and a valve housing 804. The valve housing 804 includes a diaphragm808 which is used to control movement of a valve member 806 and bias itinto a closed position when the valve mechanism 800 is in a staticstate. The diaphragm 808 is preferably located below the valve housing804 to provide a vertically moveable assembly which pressure balancesthe valve member 806 in its fully open and fully closed positions, aswell as the various partially open positions therebetween.

As shown in FIG. 22, the solenoid assembly 802 is attached to the valvehousing 804 for operating the moveable valve member 806. The valvemember 806 includes a valve stem 812 and a valve head 814, the movementof which controls the flow of exhaust gas through the valve mechanism800 when it is used as an EGR valve.

The valve housing 804 includes an inlet passage 818 and an outletpassage 820 both in communication with a central chamber 822. Thecentral chamber 822 is defined in the valve housing 804 by the innerwalls of a valve casing 824. When the valve head 814 is in the closedposition, it engages a valve seat 832 to block the flow of exhaust gasthrough the valve opening in the casing 824 to the central chamber 822.When the valve member 806 is opened, the valve head 814 is pusheddownward from a closed position 826, by the diaphragm 808, and theforces acting thereon, as discussed in detail below. The valve member806 is moveable between the closed position 826 and a fully openposition 828 (shown in lines). There are thus an infinite number ofpositions between the closed position 826 and the fully open position828 through which the valve member 806 can be positioned.

When the valve member 806 is opened or pushed away from the valve seat832, exhaust gas can pass from the exhaust gas passageway 829 throughthe valve opening 830 into the central chamber 822 where it is mixedwith an air mixture that enters the central chamber 822 though the inletpassage 818. The air exhaust gas mixture then exits the central chamber822 through the outlet passage 820 and travels to the intake manifoldand to the cylinders.

The valve stem 812 is slidably disposed in housing bearings 833supported in the side walls of the valve member 806. The valve member806 can thus reciprocate in the valve housing 804 along a generallyvertical axis as shown in FIG. 22. It should be understood, however,that the axis is merely referred to as being vertical for purposes ofillustration only and may be oriented in any direction.

As shown in FIG. 23, the diaphragm 808 is disposed below the solenoidhousing 802 and above the valve housing 804 in a diaphragm housing 834.The diaphragm housing 834 includes an upper diaphragm plate 836 lyinggenerally on the inner portion 839 of the top surface of the diaphragm808 and a lower diaphragm plate 838 lying generally on the inner portion839 of the bottom surface of the diaphragm 808. The outer portion 841 ofthe diaphragm is sandwiched and secured between the valve housing 804and the diaphragm housing 834. The upper diaphragm plate 836 is incommunication with a diaphragm retainer 840 that limits the upwardmovement of the plates 836, 838. The diaphragm retainer 840 is in turnsecured to a push rod 842 through an opening 843 in its center. The pushrod 842 reciprocates in response to movement of an armature 845 in thesolenoid assembly 810.

As shown in FIG. 22, the armature 845 and thus the valve head 814 are inthe closed position 826 with the valve head pressed up against the valveseat 832. A return spring 844 is preferably positioned between the valvehousing 804 and the lower retaining plate 838. The force of the returnspring 844 is directed upwards to bias the valve 800, which is a pushopen valve, into the closed position 826. The force of the return springhelps achieve the necessary pressure balance in accordance with thepresent invention. When the push rod 842 is forced generally downwarddue to the action of the solenoid assembly 810, the diaphragm retainer840, which is in rigid communication with the push rod 842, also movesgenerally downward against the force of the return spring 844. The forceof the diaphragm retainer 840 overcomes the spring force and moves theupper diaphragm plate 836, and thus the diaphragm 808 and the lowerdiaphragm plate 838 downward. The force applied to the push rod 842 mustbe sufficient to overcome the biasing force of the spring 844 in orderto move the diaphragm 808.

The action of the push rod 842 forces these components from a closedposition illustrated in solid lines in FIG. 23 through a range ofpartially open positions to a fully open position 828. The fully openposition is illustrated by the phantom lines. For example, the positionof the diaphragm 808′, the upper diaphragm plate 836′, and the lowerdiaphragm plate 838′ are shown by the phantom lines in FIG. 23. Throughthe movement of these components, the valve head 814 is moved away fromthe closed position 826 to allow exhaust gas to enter the centralchamber 822. The amount that the valve head 814 is opened or pushed awayfrom the valve seat amount of current passed through a wound coil 850 inthe solenoid assembly 802.

Valve mechanism 800 is preferably incorporated into an exhaust gasrecovery system by connecting it into a feed back circuit similar tothat shown in FIG. 3. When installed, the solenoid assembly 802 isconnected to an engine controller, such as the controller 50schematically illustrated in FIG. 3. The engine controller 50 is inelectrical communication with the valve sensor 849 to monitor theposition of the armature 845 and thus the position of the valve member806.

The solenoid assembly 810 includes a push rod 842 which is surrounded byand vertically moveable within wound coil 850. The amount of currentapplied to the coil 850 is controlled so that the armature 845reciprocates axially moving the valve member 814 toward and away fromthe valve seat 832 via the push rod 842 and the valve member 806. Whenenergized, the coil 850 pushes the armature 804 toward the valve body812 against the force of the expanding diaphragm 802 and the spring 844moving valve member 806 and valve head 814 away from the valve seat 826.When the coil 850 is deenergized, the valve head 826 of the valve member806 is seated against the valve seat 832.

The exhaust gas in chamber 822 acts on end plate 852 as well as thevalve head 826 of the valve member 806 producing pressure forces thatact in opposite directions. These pressure forces are balanced inaccordance with the present invention, as discussed above, and need notbe reiterated herein. Further, to the extent the valve mechanism 800contains other parts shown in the drawings but not specificallydescribed in connection with this embodiment, they are the same functionand structure as the similarly situated parts shown and described inconnection with other embodiments.

The push to open valve of the present embodiment provides at least oneadvantage in a failure mode over the pull to open valves discussedabove. This is partly because in the event that any part of this designclogs (i.e., the stem, the diaphragm retainer, etc.), the exhaustpressure, or flow forces, will naturally close the valve. The preferredfailure mode of any EGR valve is that the valve be closed to ensure theengine will not stall or burn up from excessive exhaust gas flow.Further, the location of the diaphragm 808 below the solenoid assembly802 helps reduce the amount of exhaust contaminants in the solenoid andsensor areas. It also helps reduce and prevent any high temperature atthe coil and sensor area. This is specifically an advantage with regardto diesel engines which are generally known for large amounts of carbonbuild up, and thus any reduction of carbon is a significant advantage.

Another difference between this embodiment and the prior embodiments isthe in-line casting design. With an in-line casing, the boost air fromthe intercooler can flow through the inlet opening 818 directly to thevalve member 806. This allows the valve to have a cooler medium to helpcool the solenoid and also cool the exhaust gas. Further, the desiredair stream helps direct the exhaust gas charge directly into the boostair, hence reducing the amount of contamination of the stem and bearingarea. Alternatively, this type of casting could also be manufactured toinclude the engine intake manifold and alternatively, the cylinder head.

FIGS. 24 through 26 illustrate another embodiment of an EGR valvemechanism 900 in accordance with the present invention. The valvemechanism 900 includes a sensor 902, a sensor housing 903, a valvehousing 904, and a solenoid assembly 906. The solenoid assembly 906 isattached to the valve housing 904 for operating a moveable valve member908 and the sensor housing 902 is attached to the solenoid assembly 906for detecting and controlling the movement of the valve member 908. Thevalve member 908 includes a valve stem 910 and a valve head 912 themovement of which controls the flow of exhaust gas through the valvemechanism 900.

As shown in FIG. 26, the valve housing 904 has an exhaust inlet passage918 and an exhaust outlet passage 914. The exhaust inlet passage 918 isin communication with a central chamber 920 located within the valvehousing 904 only when the solenoid is energized. The exhaust inletpassage 918 terminates at a valve seat 922. When the valve head 912 isin the closed position, it is in communication with the valve seat 922to prevent exhaust gas from flowing from the exhaust inlet passage 918into the central chamber 920. The exhaust outlet passage 914 is also incommunication with the central chamber and funnels the exhaust gasdownstream.

In operation, the valve stem 910 and valve head 912 reciprocate from theclosed position to various open positions depending upon the amount ofcurrent applied to the solenoid assembly 906. The amount of current iscontrolled by a controller 50, such as described previously inconnection with FIG. 3, which is based partly on the engine operatingconditions. The varying positions of the valve head 912 allow varyingamounts of exhaust gas to enter the central chamber 920 through theexhaust inlet passage 918. The exhaust gas that enters the centralchamber 920 then travels out the exhaust outlet passage 914 for mixingwith intake air downstream, and then through the manifold and to acylinder as is described hereinabove.

The valve stem 910 is generally hollow has an internal passage 923therein, and has at least one opening in its lower portion 924 allowingexhaust gas to flow into the internal passageway 923. The exhaust gaspasses through the internal passageway 923 of the valve stem 910 andexits through an opening in its upper portion 926 and into communicationwith a diaphragm 928. The exhaust gas exerts a pressure on the topsurface of the diaphragm 928 which is equal to and, thus in balancewith, the pressure exerted on the bottom surface of the valve head 912by the exhaust gas. As described hereinabove, other pressures are actingon the valve member 908, however, all pressure and vacuum forces arealso balanced. This provides a stable valve 900 that will not jostleopen when it is closed and will not fluctuate from one position toanother while open. This insures that the proper amount of exhaust gasis allowed into the central chamber 920 and the engine will operateproperly. The position of the valve stem 910 and valve head 912 isproportional to the amount of current in the wound coil 930. A labyrinth916 is preferably included in the internal passageway 923. The labyrinth916 separates the lower portion 924 of the valve stem 910 from the upperportion 926. The labyrinth 916 also helps reduce the temperature changesbetween the two portions 924, 926.

The wound coil 930 in the solenoid housing 906 is supported by a bobbin980 which in turn is in communication with a steel flux tube 982. Theseelements surround and encapsulate the armature 932 and the valve stem910 without any contact between the flux tube 982 and the armature 932or valve stem 910. The armature 932 surrounds a portion of the valvestem 910 while a pole piece 984 which is secured to casing of the valvehousing 904 and is located by the annular bearing 936.

The valve stem 910 is slidably disposed in a housing tube bearing 934supported in the side walls of the steel flux tube 982. An annularbearing 936 is also disposed in the valve housing 904 and surrounds andsupports the armature 932 and thus the valve stem 910. The annularbearing 936 assists in allowing the armature 932 to verticallyreciprocate and also acts as a locator to position the armature 932 withrespect to the steel flux tube 982 and the pole piece 984. The housingbearing 934 and the annular bearing 936 insure that the valve stem 910and the armature 932 reciprocate vertically with respect to the valvehousing 904 and do not become axially displaced. This arrangementensures the valve head 912 is always in line with the valve seat 922 sothat proper closure of the valve is effectuated when necessary. Priorvalves have required more complex, more expensive structures to ensureproper valve closure.

This arrangement of the valve stem 910 in the valve housing 904 leaves agap 933 between the outer surface of the armature 932 and the flux tube982. The only contact of the armature 932 with the solenoid assembly 906is at the annular ring 936 and the valve stem 910 only contacts thehousing bearing 934. It is important to prevent the magnetic armature932 from contacting the flux tube 982 and the pole piece 984 whileproperly supporting the valve stem 910 and ensuring proper closure ofthe valve head 914 with the valve seat 922.

The wound coil 930 is in electrical communication with the sensorhousing 903 and thus the controller 50. The controller 50 determines andcontrols the amount of current that is applied to the wound coil 930causing the valve stem 910 and armature 932 to reciprocate and the valvehead 912 to engage and disengage the valve seat 922. The distance thevalve head 912 is pulled away from the valve seat 922 (the amount thevalve is open) is proportional to the amount of current applied to thecoil 930.

As shown in FIG. 26, the diaphragm 928 is disposed in a diaphragmchamber 939 located in the solenoid assembly 906. The diaphragm 928 issurrounded by an upper diaphragm plate 940 lying generally on the topsurface of the diaphragm 928 and a lower diaphragm plate 942 lyinggenerally on the bottom surface of the diaphragm 928. The upperdiaphragm plate 940 is in communication with a permanent magnet 944. Thepermanent magnet 944 which reciprocates in response to movement of thearmature 932.

The permanent magnet 944 is positioned in the sensor housing 903 in atower 988. As the valve stem 910 opens and travels upward, the permanentmagnet 944 also moves upward. Conversely, when the valve is closed, thepermanent magnet 944 is reciprocated downward. The position of thepermanent magnet 944 and thus the valve is sensed to provide feedback tothe valve as needed. The sensor housing 903 has a top surface 946, apair of side surfaces 948, and a bottom surface 950 that is secured tothe solenoid housing 906 by bolts 931 or the like. The sensor 902, whichis preferably a Hall sensor or inductive sensor, as discussed in detailabove, is attached to one of the side surfaces 948 of the sensor housing903. Alternatively, the sensor 902 can also be attached to the tower 988to sense the position of the permanent magnet 944. It should beunderstood, however, that any commercially available sensor may beemployed.

The sensor housing 903 has an inner channel 953 within which thepermanent magnet 944 vertically reciprocates. The movement of thepermanent magnet 944 is limited by a spring (not shown) positionedbetween the top surface 946 of the sensor housing 903 and the permanentmagnet 944. Additionally, a pair of passageways 952 allow exhaust gasfrom the diaphragm chamber 939 to pass therethrough and contact theupper surface 954 of the permanent magnet 944. Thus, the permanentmagnet 944 is also pressure balanced to further balance the pressure andlimit any unwanted variant movements of the valve stem 910 and valvehead 912.

The valve housing 904 also preferably has at least one fluid conduit inheat transfer relationship therewith. As shown in FIG. 26, a cool fluid,such as water is passed through an inlet conduit into a fluid annulus ata first location 956 which is in a heat transfer relationship with theexhaust gas in the central chamber 920. The exhaust gas is cooled andthe resultant warmer fluid exits by an outlet conduit in communicationwith the fluid annulus at a second location 958. The fluid annulus helpkeep the exhaust gas cool and helps protect the valve mechanism 900 fromoverheating.

FIG. 27 illustrates another embodiment of an EGR valve 999 in accordancewith the present invention. Unlike the prior EGR valve 900 where thevalve housing has bottom surface 970 that is angled with respect to thetop surface 972, the bottom surface of the EGR valve 999 is parallelwith respect to the top surface 972 which allows for attachment tovarious engines or at different locations on the same engine. Thus, theEGR valve of the present invention is modular and can be incorporatedinto almost any engine, regardless of its shape or configuration.

It should be understood that the solenoid operated valve may be used inany application, particularly those where weight is an important factor.For instance, the weight of an EGR valve can be reduced from about 3pounds to about 1 pound utilizing the solenoid assembly of the presentinvention. Additionally, the solenoid current operating requirements canbe reduced from about 3.0 amps to about 1.0 amps.

While preferred embodiments of the invention have been describedhereinabove, those of ordinary skill in the art will recognize thatthese embodiments may be modified and altered without departing from thecentral spirit and scope of the invention. Thus, the embodimentsdescribed hereinabove are to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, rather than by the foregoingdescriptions, and all changes which come within the meaning and range ofequivalency of the claims are intended to be embraced herein.

What is claimed is:
 1. A solenoid operated exhaust gas recirculationvalve for an internal combustion engine, comprising: a valve housinghaving a central chamber, an inlet passage, an outlet passage, and anexhaust gas inlet passage having an inlet opening, each of said passagesbeing in fluid communication with said central chamber; a valve memberpositioned in and moveable within said central chamber, said valvemember having a hollow valve stem and a valve head, said valve headhaving at least one opening formed therein to receive exhaust gastherethrough such that it can pass into said hollow valve stem; asolenoid assembly for reciprocating said moveable valve member between aclosed position wherein said valve head engages a valve seat located atsaid exhaust gas inlet opening to prevent the flow of exhaust gas fromsaid exhaust gas inlet passage into said central chamber and a fullyopen position wherein said valve head is disposed from said valve seatallowing exhaust gas to flow from said exhaust gas inlet passage intosaid central chamber to mix with air flowing in from said inlet passage;said valve member being subjected to an initial bias which produces aforce tending to move the moveable valve member toward the closedposition; an expandable device that produces a force responsive to saidinitial bias to produce a force tending to urge the valve away from theclosed position, said expandable device having an upper and a lowersurface, whereby exhaust gas passing through said hollow valve stem,exerts a downward force on said upper surface of said expandable deviceto counteract the pressure exerted by the exhaust gas on said valvehead, whereby at all positions of the valve member between the closedand fully open positions, the pressures acting on the valve member andthe expandable device are equal so that said valve member remains in thedesired position to allow the appropriate amount of exhaust gas to entersaid central chamber.
 2. The solenoid operated valve of claim 1, whereinsaid expandable device is a diaphragm.
 3. The solenoid operated valve ofclaim 2, wherein said solenoid assembly comprises a wound coil whichreceives current from said engine controller to control the movement ofthe valve member and wherein the movement of the valve member isproportional to the amount of current in said wound coil.
 4. Thesolenoid operated valve of claim 3, wherein said sensor is a Hall fieldeffect sensor.
 5. The solenoid operated valve of claim 3, wherein saidsensor is an inductive sensor.
 6. The solenoid operated valve of claim3, wherein said moveable valve member moves away from said diaphragm toallow exhaust gas into said central chamber.
 7. The solenoid operatedvalve of claim 6, wherein said diaphragm is positioned in a diaphragmchamber which is located between said valve housing and said solenoidassembly.
 8. The solenoid operated valve of claim 7, wherein said valvestem is supported by a pair of bearings to align said valve stem withsaid valve seat.
 9. The solenoid operated valve of claim 8, wherein saiddiaphragm is attached to said valve stem in said diaphragm chamber. 10.The solenoid operated valve of claim 9, wherein said diaphragm is incommunication with a diaphragm retainer and moves in response thereto.11. The solenoid valve of claim 10, wherein said solenoid assemblyincludes a push rod that reciprocates in response to excitation of saidcoil, said push rod being in communication with said diaphragm retainer.12. The solenoid valve of claim 11, wherein said movement of said valvehead away from said valve seat is proportional to the movement of saidpush rod.
 13. The solenoid valve of claim 12, wherein said position ofsaid push rod is sensed by said position sensor to determine theposition of said valve member.
 14. The solenoid valve of claim 13,further comprising a return spring that biases said valve toward saidclosed position.
 15. The solenoid valve of claim 14, wherein saidsolenoid valve is intended for use in a diesel engine.
 16. A solenoidexhaust gas recirculation valve, comprising: a valve body having acentral chamber, an exhaust inlet passage, an outlet passage, and amoveable valve member in said central chamber controlling the flowbetween said inlet passage and said outlet passage, said valve memberincluding a valve stem and a valve head; a solenoid assembly forreciprocating the moveable valve member between an open position and aclosed position, wherein in said closed position said valve headcontacts a valve seat located at the inlet of said exhaust gas inletpassage, said solenoid assembly including a wound coil, a bobbin incontact with one surface of said wound coil, and a flux tube in contactwith a surface of said bobbin; the valve member being subjected toexhaust gas in said closed position that produces a force tending tomove the moveable poppet away from said closed position, said valvemember including an armature attached to and encapsulating a portionthereof; an expandable device which produces a force responsive to saidexhaust gas pressure for generally equalizing the force tending to movethe moveable valve member away from the closed position and maintainingthe moveable valve member in said closed position; said expandabledevice including an expandable chamber that is in fluid communicationwith the exhaust inlet passage when said valve member is closed; andsaid valve being configured such that a radial gap exists between saidsolenoid assembly and said armature for equalizing pressure in thesolenoid.
 17. The solenoid valve of claim 16, wherein an annular bearingis seated on said flux tube for vertically positioning said armature andthus said valve head.
 18. The solenoid valve of claim 17, wherein saidexpandable device includes a diaphragm that provides a spring forceacting on said valve member.
 19. The solenoid valve of claim 18, whereinsaid valve member has a passageway formed therethrough that establishesfluid communication between said expandable chamber and said exhaustinlet passage.
 20. The solenoid valve of claim 19, further comparing asensor housing attached to said solenoid assembly.
 21. The solenoidvalve of claim 20, wherein said sensor housing includes a Hall effectsensor for monitoring the position of the armature and the valve member.22. The solenoid valve of claim 20, wherein said sensor housing includesan inductance sensor for monitoring the position of the armature and thevalve member.
 23. The solenoid valve of claim 16, wherein said valve isincorporated for use in an internal combustion engine.
 24. The solenoidvalve of claim 23, wherein said outlet passageway transfers exhaust gasfrom said central chamber downstream to a mixing chamber for mixing withboost air for use in operating said engine.
 25. The solenoid valve ofclaim 16, wherein said valve housing further comprises at least onefluid annula in fluid communication with said central chamber forcooling said exhaust gas.
 26. A method of constructing and calibrating asolenoid valve assembly comprising: slidably mounting an armature,including a wound coil, and poppet within a housing to form a solenoidsubassembly; mounting a position sensor within the housing; placing thesubassembly in a test chamber; calibrating the position sensor to sensethe position of the poppet by (a) energizing the coil to the maximumrequired poppet stoke and ensuring that the poppet is in a fully openposition; and (b) deenergizing the coil to a no poppet stoke conditionand ensuring that the poppet is in a closed position abutting the valveseat; and attaching the calibrated subassembly to a base valve housingwhich is configured to mount an engine.
 27. The method of claim 26further comprising: crimping an insert to the outside of the housingprior to calibrating the position sensor.
 28. A solenoid operatedexhaust gas recirculation valve for an internal combustion engine,comprising: a valve housing having a central chamber, an exhaust gasinlet passage having an inlet opening and an outlet passage both of saidpassages in fluid communication with said central chamber; a valvemember positioned in and moveable within said central chamber, saidvalve member having a valve stem and a valve head said valve stemincluding a passageway having an opening in communication with saidexhaust gas inlet passageway; a solenoid assembly for reciprocating saidmoveable valve member between a closed position wherein said valve headengages a valve seat located at said exhaust gas inlet passage into saidcentral chamber and a fully open position wherein said valve head isdisplaced from said valve seat allowing exhaust gas to flow from saidexhaust gas inlet passage into said central chamber; said valve memberbeing subjected to an initial pressure in said closed position whichproduces a force tending to move the moveable valve member away fromsaid closed position; an expandable device that produces a forceresponsive to said initial pressure to produce a force tending to urgesaid valve head away from the closed position said expandable devicefurther having a pressure exerted thereon by said exhaust gas from saidvalve stem passageway to counteract the pressure exerted by the exhaustgas on said valve head, whereby at all positions of the valve memberbetween the closed and fully open positions, the pressures acting on thevalve member and the expandable device are equal so that the valvemember remains in the desired position to allow the appropriate amountof exhaust gas to enter said central chamber; and a sensor housingattached to said solenoid housing and including a position sensor tomonitor the position of said valve member, said position sensor being incommunication with an engine controller which controls the movement ofsaid valve member in response to operating conditions of said engine.